1.The fact that we are social animals and therefore interdependent.
2.The fact that we have “theory of mind” capacity, and can understand how the world is perceived from another person’s point of view (both literally – it probably starts with “shared gaze” capacity – and metaphorically).
3.Our language capacity, and with it, our capacity for “mental time travel” and thus the capacity to reify distant goals as they affect both others and ourselves, and thus make choices that are not solely determined by immediate personal reward.

In short, it evolved. But whether you agree with me that it evolved, or argue that it was implanted in us as a gift from God, it is undeniable that we have it, because every language has a word for “ought” AFAIK, and I know of no culture in which “duty” is an unknown concept.

– Emphasis mine, B.

But this is very problematic. First, Liz’s 1, 2, and 3 are not descriptions of source in the sense of where they came from ultimately, but only how we may realize their existence. It is simply giving an account of how we may come to realize them, or probably more accurately, how we can conceive that altruism (something that Liz said she thinks is another, perhaps better, term for morality) may be beneficial. But that seems in a roundabout way to imply one knows they are not “from above” and may potentially not actually be binding.

But, I don’t think we need to argue about that, for Liz also said, “in short, [morality] evolved”, and it seems that her three points are meant to be taken as a description of parts of that process, then.

But, if morality evolved, then it isn’t from a higher source. Even if Nature, somehow, evolved these rules apart from man, it still isn’t permissible to say that they are binding, for man is a part of Nature as much as (really, more than, being the only rational beings) anything else. So just as a man can tell Liz that she isn’t an authority over him, she being a mere co-human, a man can also say that Nature is no authority over him because he is co-Nature with Nature herself. In other words, I have the valid option of telling Nature to go take a flying leap.

But of course, Liz doesn’t believe in a teleological Nature anyway, so she would have further trouble in arguing that Nature “knows what’s best” for us. At any rate, her three points above make it sound like she is saying that these binding morals evolved from man (again, which is really the same as saying from Nature, man being part of that Nature).

So, she hasn’t shown a coherent way for these morals to be binding, for:

If man is the source of the moral law, then man governs the moral laws, and the moral laws do not govern man.

Now, the problem is what I emphasized above in quoting Liz, “it is undeniable that we have [a binding morality]”. Well, yes, it is. She has it, you have it, and both she and you know it’s binding. That isn’t the problem in itself. The problem is that when I say, “You have no grounding for your morals, to make them actually binding upon us rather than arbitrary.”, your inner “moral indignation” rises up and says, almost rightly, “Hey! I have binding morals just like you, you creep!”

But it’s only almost right. The reason isn’t that you don’t have the morals claimed, but that it is answering what wasn’t asked, or defending against what was never blamed.

Analogy:

Three Men Walking

One normal guy walks up. I ask him to jump. He does.

Another guy walks up. He is as normal as the first guy, with one exception. He is walking in the air. I ask him to jump. He tries, but cannot. He is not grounded.

A third guy walks up. He is as normal as the other two, with a different exception. He is walking on the ground, but says that he doesn’t believe in the ground. I ask him to jump. He does.

Now, when I and others say you (an atheist) have no grounding for a binding morality, you think we are claiming that you are the second “guy”. “But”, you say, “Look! I can jump just as well as you!”, and you can.

But I am not claiming you are the second guy at all. I’m claiming that you’re the third guy. You are grounded, and can jump as well as anyone. It’s not your grounding that’s the problem in the physical and practical sense, it’s your thinking about the ground that is wrong. Your thinking is irrational and incoherent on this point. You are denying the ground from which you can, still, jump.

You can jump from now until the cows come home, but until your thinking about the ground changes, you’ll never have correct understanding of an obvious fact.

You can, and do, have correct and binding morals, just as the third man can jump, but your thinking, also just like the third man, is simply incorrect.